SCAT Crank issue

[C J Murray]

John, Tom told me he was buying Shasta/JE pistons and if so there will be no problems with the wrist pins. AA wrist pins failed often and all AA sets need to be checked for the weak version wrist pin.

[Paul Lima]

Re: larger radii. That does make the crank stronger, and, in Scat's case, the choice of metal and the forging process add significantly to the strength as well.

[Brad Ripley]

The AA wrist pin thing was years ago. There is nothing wrong with any of those sets and still an excellent value for rebuilds except for all-out racing.

[Dick Weiss]

I've yet to see #2 & #3 all-aluminum main bearing shells for the 55mm journals. Then again--

[John Brooks]

Bottom end is together. What a pain these new developments are. But it went together fine. Stretching the bolts was a new experience. To make it more complicated the bolts have 8 mm heads, had three different lengths (+-.002). But starting from scratch, measuring each bolt individually worked out OK. The Carrillo tool also about .001 play when rotating it, pretty sloppy when the stretch target is .004-.005 max. I can be done with a cone anvil micrometer also, and it may have better clearance.

I do not have one, but an SNAP-ON Torque Adapter, 8 mm, 12-Point 3/8 drive offset torque adapter, box wrench, (FRDHM8) might make this process easier if you do allot of these. Since the final torque does not matter. You can put on the off set wrench and the stretch measuring tool at the same time and torque the rod bolt and see the stretch dial as the bolt elongates.

Very little torque required~ 120-135 in pounds in these rods. 5 in-lbs = about 0.0003 on most of the bolts, but it's not linear. Most of my TQ-Wrenches started at 150 in-lbs. I had to use and old one for aircraft avionics to get that far down the 0-150 scale. Not as easy as OEM parts, but much better.

But the bottom end is done. It has .015 side clearance on the rods, good fit and very pretty. Tomorrow the Shasta PC and get ready for the new heads. And the cam drive gear had 8-10 big strike marks from Harry's big hammer/screwdriver method of seating the gear. But a Std Std case with two rebuilds and 100k miles on the last one, Harry did well on this one.

More to follow

[Martin Benade]

According to my math that's only about 10 ft/lbs to get about .007" stretch? Can that possibly be enough/correct? I am just wondering out loud, I don't know the answer.

[John Brooks]

Martin

I agree, but the max NTE torque on these S4 1/4-28 bolts is 215 In-Lbs. about >18 ft pounds. The don't start to stretch until around 15-16, and the elongation is not linear or the same between bolts. Some rods were 20 the other side was 23, with them both starting at 15 alternating back and forth. and both ending up with the same indicated elongation.

I am a 35 foot pound, new rod nut kind of old guy. These stretch bolt start to elongate about 15 In-Lbs. I had a pretty good accurate torque wrench. I would bump the torque 3-5 In-lb, measure, bump again Measure, each bolt took maybe 8-10 measurements. This was much more tedious than stock rods, but much stronger and lighter.

The best part was different starting length on several bolts. You sneak up on the stretch, no two bolts had the same final torque. I would watch the little serrations on the end of metric socket, in a reflected glare from the light and tighten 1 line at a time when it got close to .004. You can stretch these little bolts .0003 with a single degree of rotation.

http://www.cp-carrillo.com/file/6995-St ... ctions.pdf

[Neil Bardsley]

If, like me, you had never heard of bolt stretching

http://www.hotrod.com/articles/using-ro ... etch-tool/

[Vic Skirmants]

John; I thought the new recommended stretch was more like .005" minimum. I use .005" up to .006" on the race bolts.

[Martin Benade]

I know torque is not the thing here, but ten-ish ft/lbs is reasonable?

[C J Murray]

I would not use an offset adapter wrench on such a precise job. A 12 point US(3/8"?) fits perfectly on the bolts. The bolts must have the Carrillo lube on the threads and under the head. Each bolt gets finger tightened into the rod after being first fully seated via wrench. The finger tight bolt is measured and zeroed on the gauge. Every bolt I have torqued has had the correct stretch when fairly close to the maximum allowed torque so I always first torque fairly high but safely under the max to take the first stretch measurement. This saves some steps. The first time using these small bolts is a little unnerving but you learn that they are like everything else only the torque numbers are lower.

When you checked the #2 main in the case half, endplay set, was there interference? I ask because I have never had a problem there and I spoke yesterday to a shop that has used many Scat cranks and never had that problem.

[C J Murray]

I know torque is not the thing here, but ten-ish ft/lbs is reasonable?

They are good to at least 9000rpm. Surprisingly, as a bolt is made smaller in diameter the centerline can be moved closer to the force being controlled and being closer to that force the force has less leverage to use against the bolt. In some cases a small fastener closer to the crank journal could be stronger or at least stronger than you would think. If our engines had more space inside Carrillo probably would have used 5/16" bolts but you still have to install them with a stretch gauge to do the job right. You can get rods to convert to Chevy rod bearings that have 5/16" bolts.

[Mike Smith]

Brad -The AA wrist pin thing was years ago. There is nothing wrong with any of those sets and still an excellent value for rebuilds except for all-out racing.

Agreed Brad - we have fitted over 30 sets to date without any problems

[Adam Wright]

Brad -The AA wrist pin thing was years ago. There is nothing wrong with any of those sets and still an excellent value for rebuilds except for all-out racing.

Agreed Brad - we have fitted over 30 sets to date without any problems

But with that in mind I would recommend anyone using AA pistons to get them directly from AA, not from one of the re-sellers or EBAY sellers who may have an old set, even un-knowingly.

[C J Murray]

Brad -The AA wrist pin thing was years ago. There is nothing wrong with any of those sets and still an excellent value for rebuilds except for all-out racing.

Agreed Brad - we have fitted over 30 sets to date without any problems

I believe a failure was reported here within the last 2 years. I strongly suspect that that set sat on a shelf somewhere for a long time before being sold. Just be aware and ask questions of your supplier.

I have used AA P&C sets a couple of times and they have worked fine. The aluminum finned version of cylinders that I have used do not fit our engines until you grind away some fins to make clearance in a few places.

The AA iron barrel/cast piston sets are good for most street cars but the Shasta durabar barrel/JE piston sets are much better. You get what you pay for.